1. Field of the Invention
The preset invention relates to a motor driving device and a driving method thereof, and more particularly relates to a motor driving device and a driving method thereof with the lowest rotating speed setting.
2. Description of the Prior Art
The conventional method is to implement Pulse Width Modulation (PWM) to control the motor driving, but it cannot have the function to adjust the rotating speed curve. The corresponding rotating speed of the motor output is based on the input Duty cycle. For example, please refer to FIG. 1, which is an output curve view illustrating the conventional PWM motor driving. As shown in FIG. 1, the Duty cycle of the PWM is 0% to 100%. When the Duty cycle of the PWM is 50%, the corresponding motor will output 50% rotating speed. Therefore, the control curve of the motor rotating speed will be a linear curve.
In order to achieve the lowest heat releasing request and reduce the noise signal or noise at the same motor loading, the motor is required to be in a predetermined speed when the Duty cycle of the PWM is lower to a predetermined value instead of stopping the motor rotating when the Duty cycle of the PWM is lower than the predetermined value.
However, when the user would like to change the motor rotating speed in accordance with the practical operation, the common method is to change the input PWM Duty cycle or the coil design of the motor. However, both of the methods are difficult to be operated practically. For example: if it would like to change the PWM Duty cycle inputted by the controller in accordance with the practical operation, the control method of the whole system is required to be changed; if it would like to change the coil of the motor, the motor is required to be replaced.
Therefore, a motor speed adjustable motor driving device and a driving method thereof is provided in the present invention. Not only adjusting a voltage among a highest setting voltage signal (VH), a lowest setting voltage signal (VL) and a triangular signal (TRI) but also adjusting the lowest rotating speed setting voltage signal to maintain the lowest torque of the motor to satisfy the request of the lowest heat releasing, the motor driving device can be adjusted to have the function of changing motor rotating speed and include the function of setting the lowest rotating speed so as to increase the implementing flexibility of the motor rotating speed controlled by the PWM.